ES2872008T3 - Lithium-ion battery with improved thermal stability - Google Patents

Abstract

A method of forming a cathode comprising: (a) mixing a lithium metal oxide and a lithium metal phosphate in a solvent, wherein the lithium metal phosphate has a volume fraction of secondary particles having a size of 0.1 to 3 microns which is 5 to 100%, based on the total content of the lithium metal phosphate; and where the lithium metal phosphate has the formula: Li1+aMnbFecM1-b-cPO4, Formula (I) where: a is a number from 0.0 to 0.2, and preferably from 0.0 to 0.15, and more preferably from 0 to 0.12; b is a number from 0.05 to 0.95 and preferably from 0.1 to 0.9 and more preferably from 0.2 to 0.8; c is a number from 0.05 to 0.95 and preferably from 0.1 to 0.9 and more preferably from 0.2 to 0.8; and (1bc) is from 0.0 to 0.2, and preferably from 0.0 to 0.15, and more preferably from 0.0 to 0.12, where M is a metal ion selected from one or more of magnesium, calcium, strontium, cobalt, titanium, zirconium, molybdenum, vanadium, niobium, nickel, scandium, chromium, copper, zinc, beryllium, lanthanum, and aluminum, and lithium metal oxide has the following formula: LiXNiyMnzCo(2- xyz)DwO2, Formula (III), or LiXNiyMnzCo(2-xyz) O2 where: x is a number from 0.9 to 1.15, and preferably from 0.95 to 0.110, and more preferably from 0.98 to 1 .08; y is a number from 0.05 to 0.95, and preferably from 0.2 to 0.95, and more preferably from 0.3 to 0.95; z is a number from 0.05 to 0.95, and preferably from 0.05 to 0.8, and more preferably from 0.05 to 0.7; (2xyz) is from 0.05 to 0.95, and preferably from 0.05 to 0.8, and more preferably from 0.5 to 0.7, and w is from 0 to 0.4, and preferably from 0 to 0.3, and where D, when present, is selected from the group consisting of B, Al, Ti, Mg, Nb, Si, Fe, V, Cr Cu, Zn, Ga and W, and is preferably selected from group consisting of Al, Ti, Mg and Nb (b) coating the mixture from step (a) on a metal foil; and (c) removing the solvent to form the cathode in which a D50 of the lithium metal phosphate is equal to or less than 3.5 microns.

Description

DESCRIPTION

Lithium-ion battery with improved thermal stability

Field of the invention

The invention relates to a method for making lithium ion batteries (LIB) and improved cathodes for making LIB. In particular, the invention relates to lithium ion batteries composed of lithium metal oxide cathode materials in which improved battery characteristics such as increased cycle life, safety and speed capacity can be achieved.

Background of the invention

Lithium-ion batteries have been used for the past two decades in portable electronic equipment and, more recently, in hybrid or electric vehicles. Initially, lithium-ion batteries first used lithium cobalt oxide cathodes. Due to expense, toxicological problems, and limited energy capacity, other cathode materials have been or are being developed.

One class of materials that has been developed and used commercially are lithium metal oxides composed of two or more of nickel, manganese, and cobalt. These materials generally show a layered structure with a singular rhombohedral phase in which high initial specific charge capacities (~ 170 mAh / g) have been achieved when charged at voltages of approximately 4.2 volts versus Li / Li +. Unfortunately, these materials have suffered from a short life cycle and safety issues related to the evolution of oxygen under certain conditions that have led to fires.

Li / Li + represents the redox potential of the lithium reference electrode, which is defined as 0 volts by convention. Consequently, when using an anode other than Li metal, these voltages would be lowered to account for the potential difference between this other anode and the Li metal. Illustratively, a fully charged graphite anode has a potential of approximately 0.1 V versus Li / Li +. Therefore, when charging the cathode in a battery with a graphite anode at 4.25 V vs. Li / Li +, the cell voltage will be about 4.15 V.

The life cycle is generally taken as the number of cycles (charge-discharge) before reaching a specific capacity that is 80% of the initial specific capacity. Each cycle for these materials is typically between the 4.2 volts and 2 volts mentioned above. These batteries have also suffered inconsistencies in performance from one battery or cell to another, despite being made from the same materials.

To solve some of the problems, the art has described numerous coatings, dopants as well as mixtures of other more stable cathode materials such as lithium iron phosphate. Examples include those described in US Patent Publication Nos. 2004/0005265; 2004/0096743; 2006/0194112; and 2009/0305132; WO Patent Applications No. 2008/088180; 2008/091074; 2009/057834; and 2013/016426 and Japanese Patent No. 9035715A1. Unfortunately, although these may have improved the safety of LIBs contained in cathode materials composed of lithium metal oxides containing nickel, manganese, cobalt, or a combination thereof, the life cycle, battery capacity or capacity at high download speeds did not improve.

Consequently, it would be desirable to provide a method of forming LIBs having cathodes composed of lithium metal oxides of nickel, manganese, cobalt, or combinations thereof that results in more consistent performance, improved life cycle, and increased retention. of power capacity at faster upload / download speeds while enhancing the security of such LIBs.

Compendium of the invention

Aspects of the invention are based on the surprising discovery that cathode materials, and therefore LIBS, having improved thermal stability can be produced from a cathode material that is composed of a mixture of an oxide of lithium metal and a lithium metal phosphate in which the lithium metal phosphate comprises a volume fraction of secondary particles having a size of 0.1 to 3 microns (pm) that is 5 to 100%, based in the total content of lithium metal phosphate. More specifically, the inventors have discovered that cathodes comprising lithium metal phosphates having the listed secondary particle ranges help provide cathode materials that are capable of passing the nail penetration test without generating smoke or flames.

Transitional lithium metal oxides, such as lithium-nickel-manganese-cobalt oxide (LNMCO) with a formula of LixNiyMnzCo ¹ -y-zO ² where x = 0.9-1.1, y = 0.05 <y <0.95, and z = 0.05-0.95, are becoming increasingly attractive for use in energy storage applications, such as LIB applications for electric vehicles. LNMCO generally has higher capacity and higher press density than spinel-type lithium manganese oxide (LiMn2O4) and olivine-type lithium transition metal phosphate (LiMPO4). Consequently, it is believed that LNMCO can provide comparable capacity to lithium cobalt oxide (LiCoO ² ), as well as being more environmentally friendly and also providing better cost effectiveness. However, the thermal stability of LNMCO and other Lithium metal oxides present challenges for the use of these materials in LIB.

In one aspect, embodiments of the present invention provide a method of forming a cathode comprising the steps of (a) mixing a lithium metal oxide and a lithium metal phosphate in a solvent, wherein the metal phosphate lithium comprises a volume fraction of secondary particles having a size of 0.1 to 3 pm that is 5 to 100%, based on the total content of lithium metal phosphate;

and where lithium metal phosphate has the formula:

Li1 + aMnbFecM1-b-cPÜ4, Formula (I)

where:

a is a number from 0.0 to 0.2, and preferably from 0.0 to 0.15, and more preferably from 0 to 0.12;

b is a number from 0.05 to 0.95 and preferably from 0.1 to 0.9 and more preferably from 0.2 to 0.8;

c is a number from 0.05 to 0.95 and preferably from 0.1 to 0.9 and more preferably from 0.2 to 0.8; and

(1-b-c) is 0.0 to 0.2, and preferably 0.0 to 0.15, and more preferably 0.0 to 0.12,

where M is a metal ion selected from one or more of magnesium, calcium, strontium, cobalt, titanium, zirconium, molybdenum, vanadium, niobium, nickel, scandium, chromium, copper, zinc, beryllium, lanthanum and aluminum, and the oxide of lithium metal has the following formula:

LixNiyMnzCo ( ² -xyz) DwO ² , Formula (III),

or

LixNiyMnzCo ( ² -xyz) O ² ,

where:

x is a number from 0.9 to 1.15, and preferably from 0.95 to 0.110, and more preferably from 0.98 to 1.08;

y is a number from 0.05 to 0.95, and preferably from 0.2 to 0.95, and more preferably from 0.3 to 0.95;

z is a number from 0.05 to 0.95, and preferably from 0.05 to 0.8, and more preferably from 0.05 to 0.7;

(2-x-y-z) is 0.05 to 0.95, and preferably 0.05 to 0.8, and more preferably 0.5 to 0.7, and

w is 0 to 0.4, and preferably 0 to 0.3, and where D, when present, is selected from the group consisting of B, Al, Ti, Mg, Nb, Si, Fe, V, Cr Cu, Zn, Ga and W, and is preferably selected from the group consisting of Al, Ti, Mg and Nb (b) coating the mixture of step (a) on a metal foil; and (c) removing the solvent to form the cathode, wherein a D50 of the lithium metal phosphate is equal to or less than 3.5 microns.

The method can also include one or more of the steps of depositing the cathode material on a conductive substrate, such as a metal foil; pressing the cathode material and forming the cathode into an energy storage device, such as a lithium ion battery.

A further aspect of the invention relates to the cathode material comprising a lithium metal oxide and lithium metal phosphate in a solvent, wherein the lithium metal phosphate has a volume fraction of particles having a size 0.1 to 3 pm which is 5 to 100%, wherein a D50 of lithium metal phosphate is equal to or less than 3.5 microns

and where lithium metal phosphate has the formula:

Li1 + aMnbFecM1-b-c, PO4, Formula (I)

where:

a is a number from 0.0 to 0.2, and preferably from 0.0 to 0.15, and more preferably from 0 to 0.12;

b is a number from 0.05 to 0.95 and preferably from 0.1 to 0.9 and more preferably from 0.2 to 0.8;

c is a number from 0.05 to 0.95 and preferably from 0.1 to 0.9 and more preferably from 0.2 to 0.8; and

(1-b-c) is 0.0 to 0.2, and preferably 0.0 to 0.15, and more preferably 0.0 to 0.12,

where M is a metal ion selected from one or more of magnesium, calcium, strontium, cobalt, titanium, zirconium, Molybdenum, vanadium, niobium, nickel, scandium, chromium, copper, zinc, beryllium, lanthanum, and aluminum, and lithium metal oxide has the following formula:

LiXNiyMnzCo ( ² -xyz) DwO ² , Formula (NI),

or

LiXNiyM nzCo (2-x-y-z) O2,

where:

x is a number from 0.9 to 1.15, and preferably from 0.95 to 0.110, and more preferably from 0.98 to 1.08;

y is a number from 0.05 to 0.95, and preferably from 0.2 to 0.95, and more preferably from 0.3 to 0.95;

z is a number from 0.05 to 0.95, and preferably from 0.05 to 0.8, and more preferably from 0.05 to 0.7;

(2-x-y-z) is 0.05 to 0.95, and preferably 0.05 to 0.8, and more preferably 0.5 to 0.7, and

w is 0 to 0.4, and preferably 0 to 0.3, and where D, when present, is selected from the group consisting of B, Al, Ti, Mg, Nb, Si, Fe, V, Cr Cu, Zn, Ga and W, and is preferably selected from the group consisting of Al, Ti, Mg and Nb. As noted above, the inventors have discovered embodiments of the invention that provide cathodes that have improved thermal stability and safety. In particular, the inventors have also discovered that the thermal stability of cathodes comprising LNMCO can be improved by using a lithium metal phosphate comprising a volume fraction of particles having a size of 0.1 to 3 µm which is 5 to 100%, based on total lithium metal phosphate content.

In one embodiment, the lithium metal phosphate may comprise a volume fraction of secondary particles having a size of 0.1 to 3 µm or less is at least 20%, and in particular, a lithium metal phosphate that It comprises a volume fraction of secondary particles having a size of 0.1 to 3 µm is at least 50%. In some embodiments, the lithium metal phosphate may comprise a D50 particle distribution that is greater than 0.1 µm and equal to or less than 2.5, 2.6, 2.7, 2.8, 2, 9, 3.0, 3.1, 3.2, 3.3, 3.4 | um. Preferably, the lithium metal phosphate has a D50 that is between 0.1 and 3.1 µm.

According to the invention, lithium metal phosphate has the formula Lh + aMnbFecM1-b-cPO4, where

a is a number from 0.0 to 0.2, and preferably from 0.0 to 0.15, and more preferably from 0 to 0.12;

b is a number from 0.05 to 0.95 and preferably from 0.1 to 0.9 and more preferably from 0.2 to 0.8;

c is a number from 0.05 to 0.95 and preferably from 0.1 to 0.9 and more preferably from 0.2 to 0.8; and

(1-bc) is 0.0 to 0.2, and preferably 0.0 to 0.15, and more preferably 0.0 to 0.12, and where M is a metal ion selected from one or plus magnesium, calcium, strontium, cobalt, titanium, zirconium, molybdenum, vanadium, niobium, nickel, scandium, chromium, copper, zinc, beryllium, lanthanum and aluminum.

In one embodiment, the lithium metal oxide has the formula LixNiy MnzCo ( ² -xyz) DwO ² , where

x is a number from 0.9 to 1.15, and preferably from 0.95 to 0.110, and more preferably from 0.98 to 1.08;

y is a number from 0.05 to 0.95, and preferably from 0.2 to 0.95, and more preferably from 0.3 to 0.95;

z is a number from 0.05 to 0.95, and preferably from 0.05 to 0.8, and more preferably from 0.05 to 0.7;

(2-x-y-z) is 0.05 to 0.95, and preferably 0.05 to 0.8, and more preferably 0.5 to 0.7; and

w is 0 to 0.4, and preferably 0 to 0.3, and where D is selected from the group consisting of B, Al, Ti, Mg, Nb, Si, Fe, V, Cr Cu, Zn, Ga and W, and is preferably selected from the group consisting of Al, Ti, Mg and Nb.

In one embodiment, the lithium metal oxide has the formula LixNiy MnzCo ( ² -xyz) O ² where

x is a number from 0.9 to 1.15, and preferably from 0.95 to 0.110, and more preferably from 0.98 to 1.08;

y is a number from 0.05 to 0.95, and preferably from 0.2 to 0.95, and more preferably from 0.3 to 0.95;

z is a number from 0.05 to 0.95, and preferably from 0.05 to 0.8, and more preferably from 0.05 to 0.7; and

(2-x-y-z) is 0.05 to 0.95, and preferably 0.05 to 0.8, and more preferably 0.5 to 0.7.

Aspects of the invention also relate to a lithium ion battery comprising a cathode according to with embodiments of the invention.

Detailed description of the invention

The inventors have now surprisingly discovered that the thermal stability and safety of cathode materials comprising a lithium metal oxide, such as LNMCO, and a lithium metal phosphate in which the lithium metal phosphate comprises a fraction in volume of particles having a size of 0.1 to 3 gm that is, 5 to 100%, based on the total content of lithium metal phosphate.

Lithium metal phosphates that can be used in aspects of the invention generally include any that are capable of inserting and extracting lithium. Suitable lithium metal phosphates include, for example, those described in US Patent Nos. 5910382; 6514640; 5871866; 6632566; 7217474; 6528033; 6716372; 6749967, 6746799; 6811924; 6814764; 7029795; 7087346; 6855273; 7601318; 7338734; and 2010/0327223.

A preferred lithium metal phosphate is one in which the majority of the metal is Mn, which has a higher redox potential, for example, than the iron in lithium iron phosphate. The higher redox potential of Mn has been found to be useful in making a LIB with smooth or uniform discharge curves when mixed with lithium metal oxides. According to the invention, lithium metal phosphate is one that has an empirical formula:

Li ¹ + a MnbFecM1-b-cPO4, Formula (I)

where

a is a number from 0.0 to 0.2, and preferably from 0.0 to 0.15, and more preferably from 0 to 0.12;

b is a number from 0.05 to 0.95 and preferably from 0.1 to 0.9 and more preferably from 0.2 to 0.8;

c is a number from 0.05 to 0.95 and preferably from 0.1 to 0.9 and more preferably from 0.2 to 0.8; and

(1-b-c) is 0.0 to 0.2, and preferably 0.0 to 0.15, and more preferably 0.0 to 0.12.

M is a metal ion selected from one or more of magnesium, calcium, strontium, cobalt, titanium, zirconium, molybdenum, vanadium, niobium, nickel, scandium, chromium, copper, zinc, beryllium, lanthanum, and aluminum. In some embodiments, at least a portion of the lithium metal phosphate has an olivine backbone. It is further preferred that M is magnesium, cobalt, or a combination thereof. This particular phosphate material has been found to not only improve life cycle even though it has a high Mn concentration, but it also does not negatively affect battery voltage discharge profiles as metal phosphates do. lithium with high iron content. Additional lithium metal phosphates may include those that have an empirical formula:

LiaMnbFecMdPO4: Formula (II),

where

a is a number from 0.85 to 1.15;

b is 0.51 to 0.95;

c is 0.05 to 0.49;

d is 0.000 to 0.1;

M is a metal ion selected from one or more of magnesium, calcium, strontium, cobalt, titanium, zirconium, molybdenum, vanadium, niobium, nickel, scandium, chromium, copper, zinc, beryllium, lanthanum, and aluminum. In one embodiment, the lithium metal phosphate can be one having an empirical formula LiaMnbFecMdPO4, where

a is a number from 0.85 to 1.15;

b is 0.65 to 0.95;

c is 0.049 to 0.349;

d is 0.001 to 0.1;

2.75 <(a 2b 2c dV) <3.10, where V is the valence of M, and M is a metal ion selected from one or more of magnesium, calcium, strontium, cobalt, titanium, zirconium, molybdenum, vanadium, niobium, nickel, scandium, chromium, copper, zinc, beryllium, lanthanum and aluminum, and furthermore in which at least a part of the lithium metal phosphate has an olivine structure.

According to the invention, lithium metal phosphate has a volume fraction of secondary particles that have a size from 0.1 gm to 3 microns (gm) which is 5 to 100% based on the total content of the lithium metal phosphate. Preferably, the volume fraction of secondary particles having a size of 0.1 gm to 3 gm is 10 to 90%, and more preferably 15 to 80%, based on the total content of lithium metal phosphate.

Lithium metal phosphate has a volume fraction of secondary particles having a size of 0.1 to 3 gm that is at least 5%, based on the total content of the lithium metal phosphate. For example, lithium metal phosphate preferably includes a volume fraction of secondary particles having a size of 0.1 to 3 gm that is at least 10%, at least 15%, at least 20%, at least 22%. , at least 24%, at least 26%, at least 28%, at least 30%, at least 32%, at least 34%, at least 36%, at least 38%, at least 40%, at least 42% , at least 44%, at least 46%, at least 48% and at least 50% based on the total content of the lithium metal phosphate.

The volume fraction of secondary particles can also be characterized in terms of the particle distribution of the secondary particles. For example, in embodiments of the present invention, lithium metal phosphate generally has a mean secondary particle size (D50) of 0.1 microns to 3.5 microns. The particle size distribution is given by the D10, D50 and D90 particle sizes. D10 is the size where 10% of the particles are smallest, D50 is the size where 50% of the particles are smallest, and D90 is the size of the particles where 90% of the particles are smallest in a distribution. given by number. The D10 is typically equal to or less than 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1.0 microns. The D50 is at least 0.1 gm, and typically is at least equal to or less than 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3, 2, 3.3, 3.4 or 3.5 microns. The D90 is typically equal to or less than 7, 8, 9, 10, 11, 12, 13, 14, or 15 microns.

The term "secondary particles", as used herein, refers to nanoscale primary particles that have agglomerated to form larger particles that are about 0.1 microns or more in size. Thus, secondary particles refer to agglomerations of nanoscale particles and therefore exclude primary particles that are less than 0.1 gm in size.

Particle size can be measured by any appropriate method known in the art. For example, particle size can be measured using laser diffraction.

In one embodiment, the lithium metal phosphate may comprise a mixture of two different lithium metal phosphates in which one of the lithium metal phosphates may not meet the required particle sizes as discussed. For example, in one embodiment, the lithium metal phosphate may comprise a mixture of two or more lithium metal phosphates with at least one first lithium metal phosphate having a volume fraction of particles having a size of 0 , 1 to 3 gm that is 5 to 100%, and at least one second lithium metal phosphate that has a volume fraction of particles having a size of 0.1 to 3 gm that is 0% or substantially close to 0% as long as the lithium metal phosphate mixture has a volume fraction of secondary particles having a size of 0.1 to 3 gm or less that is between 5 and 100%. Preferably, said lithium metal phosphate mixture has a volume fraction of particles having a size of 0.1 to 3 gm which is at least 10%, at least 15%, at least 20%, at least 22%, at least 24%, at least 26%, at least 28% or at least 30% or more.

The lithium metal oxide can be any that is capable of inserting and extracting lithium into a LIB as known in the art. Examples of such lithium metal oxides include those described in US Patent Nos. 5858324; 6368749; 6964828; and EP Patent Nos. 0782206; 1296391; 0813256; 1295851; 0849817; 0872450; and 0918041 and JP Patent No. 11-307094. Preferred metal oxides include those having a layered structure of the Rm3 type, also called O3 structures that have a singular phase.

Additional lithium metal oxides that can be used in embodiments include those described by US Patent No. 6964828. A preferred lithium metal oxide may have the following empirical formula.

LixNiy MnzCo ( ² -xyz) DwO ² : Formula (III),

where

x is a number from 0.9 to 1.15, and preferably from 0.95 to 0.110, and more preferably from 0.98 to 1.08;

y is a number from 0.05 to 0.95, and preferably from 0.2 to 0.95, and more preferably from 0.3 to 0.95;

z is a number from 0.05 to 0.95, and preferably from 0.05 to 0.8, and more preferably from 0.05 to 0.7;

(2-x-y-z) is 0.05 to 0.95, and preferably 0.05 to 0.8, and more preferably 0.5 to 0.7; and

w is 0 to 0.4 and preferably 0 to 0.3. D can be any one or more of Al, Ti, Mg, Nb, or any other metal suitable for use as a doping element. In one embodiment, D is selected from the group consisting of B, Al, Ti, Mg, Nb, Si, Fe, V, Cr, Cu, Zn, Ga, and W.

A preferred lithium metal oxide has the empirical formulas LixNiy MnzCo ( ² -xyz) O ² , where x, y, and z are the same as described above.

Desirable lithium metal oxides can also include those of the following formula.

LixCoyMnz (D) wNii- (y + z + d) O ² : Formula (IV)

where (D) indicates a metal other than Co, Mn, or Ni and x is greater than 0 to 1.2; y is 0.1 to 0.5, z is 0.05 to 0.4, and w is 0 to 0.4, and b + c + d is 0.15 to 0.5. D is preferably B, Al, Si, Fe, V, Cr, Cu, Zn, Ga and W. Preferably "x" is less than 1.1 and more preferably less than 1.05. It is understood that LIBs made from such cathode materials are assembled in the discharged state (that is, the lithium is present in the lithium metal oxide "x ~ 1" and is then extracted and inserted into the anode when charging the LIB for the first time). It is also understood that more than one lithium metal oxide can be used in which the lithium metal oxide may differ in chemistry, primary particle size, or the like.

A further example of a lithium metal oxide that can be used in embodiments of the present invention is LiCoO ² .

The weight percent amount of lithium metal phosphate in the active cathode material generally ranges from 5 to 90 weight percent, based on the total weight percent of the cathode material. Preferably, the amount of lithium metal phosphate in the active cathode material is 5 to 60 percent by weight, and more preferably, 10 to 50 percent by weight, based on the total weight percent of the cathode material. .

The weight percent amount of lithium metal oxide in the active cathode material generally ranges from 10 to 95 weight percent, based on the total weight percent of the cathode material. Preferably, the amount of lithium metal oxide in the active cathode material is 30 to 90 percent by weight, and more preferably, 50 to 85 percent by weight, based on the total weight percent of the cathode material. .

Lithium metal phosphate, depending on the particular metals, may advantageously have an electronic coating thereon. The coating is generally present in an amount of 0.5% by weight to 20% by weight of the lithium metal phosphate and said coating. It is desirable to have as little coating as possible, and as such the amount is desirably at most 10%, 8%, 5%, or even 3%. Typically the coating is carbonaceous and can include graphitic carbon, amorphous carbon, or combinations thereof. A desirable carbon coating may be that resulting from the carburization of an organic compound such as those known in the art, examples being phenol, formaldehydes, sugars (eg, lactose, glucose, and fructose), starches, and celluloses.

In one embodiment, it may be desirable to mix the lithium metal oxide and the lithium metal phosphate in a solvent to allow a uniform mixture to form. The solvent can be any suitable solvent as known in the art and are typically polar and non-polar organic solvents with low water content (eg 500 ppm or less and preferably less than 100, 50, 10 or even 1 ppm). Examples of useful solvents include organic solvents such as n-methyl pyrrolidone.

(NMP) and acetone and polar solvents such as water and those described by Jin Chong, et al., Journal of Power Sources 196 (2011) pp. 7707-7714.

The amount of solids (lithium metal oxide and phosphate) can be any useful amount. Typically, the amount is 10% to 90% by volume of the solvent and can be from at least 20% or 30% to at most 80% or 70%.

In some embodiments, it may be desirable for the mixing to be performed under conditions of low shear mixing techniques such as single paddle mixers with or without baffles. Generally, the shear rate is at most around 5000 s-1 and is generally from about 1 s-1 to about 1000 s-1. Other known additives useful for casting suspensions onto sheets can be used, such as suitable dispersants, lubricants, binders and water scavengers.

Mixing is done over time to disperse the lithium metal oxide and lithium metal phosphate sufficiently to achieve the desired results. Typically the time can be from several minutes to any time possible, such as days or hours.

The mixture can then be coated onto a metal foil that is useful for making battery electrodes such as aluminum, carbon-coated aluminum, etched aluminum, nickel, copper, gold, silver, platinum, and alloys of the aforementioned or combinations thereof. and include those described in Hsien-Chang Wu et al., Journal of Power Sources 197 (2012) pp. 301-304.

Coating of the suspension can be accomplished by any useful technique such as those known in the art. Typically the method employed is a scraper blade casting in a desired gap.

The solvent is then removed to form the cathode. Removal can be any suitable method such as evaporation with or without heating under static or flowing air or other suitable atmosphere such as dry air, inert atmosphere (nitrogen or inert gas such as noble gas) or vacuum. If heating is employed, the temperature is useful for the particular solvent employed and may be 30 to 500 ° C, but preferably 50 to 150 ° C. The time can be any suitable time, such as from several minutes to days or hours. The heating can be any useful heating such as resistance, convection, microwave, induction, or any known heating method.

In one embodiment, after the solvent has been removed, the cathode is further pressed. This pressing in many cases refers to calendering in the art to further increase the density of the lithium metal oxide / lithium metal phosphate coating on the metal foil. Typically, calendering is done by passing the cathode through a roller press with a fixed gap to obtain a cathode with a uniform thickness. The cathode can pass through the roller press multiple times with changing gaps or the same gap depending on the behavior of the coating. When pressing, it is desirable to distort only the lithium metal phosphate secondary particles and not have any appreciable changes, such as fracture of the lithium metal phosphate secondary particles. Generally, this corresponds to a pressure that is at most about 500 MPa and is desirable at most about 250, 180, 170 or 160 MPa at a low pressure that can be at least about 10 MPa. Also, the pressure should not be so great as to cause fracture of any electronically conductive coating of the lithium metal phosphate and not so high that the density of the coating is too high, for example, the electrolyte used in the battery has difficulty to wet the cathode sufficiently to achieve the desired results.

Typically the coating has a% theoretical density that is 40% to 85% of the theoretical density (60% to 15% porous). It is desirable that the theoretical density is at least 45%, 50% or even 55% to 80%, 75% or even 70%.

The cathode is useful for making improved LIBs and when making such LIBs, suitable anode materials include, for example, carbonaceous materials such as natural or artificial graphite, carbonized pitch, carbon fibers, graphitized mesophase microspheres, furnace black, black acetylene and various other graphitized materials. Suitable carbonaceous anodes and methods for making them are described, for example, in US Patent No. 7,169,511. Other suitable anode materials include metallic lithium, lithium alloys, other lithium compounds such as lithium titanate, and metal oxides such as TiO ² , SnO ^2, and SiO ² , as well as materials such as Si, Sn, or Sb. The anode can be manufactured using one or more suitable anode materials.

The LIB spacer is generally a non-conductive material. It must not be reactive or soluble in the electrolyte solution or any of the components of the electrolyte solution under operating conditions, but it must allow lithium ion transport between the anode and the cathode. Polymeric spacers are generally suitable. Examples of suitable polymers to form the spacer include polyethylene, polypropylene, polybutene-1, poly-3-methylpentene, ethylene-propylene copolymers, polytetrafluoroethylene, polystyrene, polymethylmethacrylate, polydimethylsiloxane, polyethersulfones, and the like.

Generally, the battery electrolyte solution has a lithium salt concentration of at least 0.1 mole / liter (0.1 M), preferably at least 0.5 mole / liter (0.5 M), more preferably at least 0.75 moles / liter (0.75 M), preferably up to 3 moles / liter (3.0 M), and more preferably up to 1.5 moles / liter (1.5 M). The lithium salt can be any that is suitable for battery use, including lithium salts such as LiAsF6, LiPF6, LiPF4 (C2O4), LiPF2 (C2CO4) 2, LiBF4, LiB (C2O4) 2, LiBF2 (C2O4), LiClO4, LiBrO4, LiIO4, LiB (C6Ha) 4, UCH ³ SO ³ , LiN (SO ² C ² Fa) ² and LiCF3SO3. The solvent in the battery electrolyte solution can be or include, for example, a cyclic alkylene carbonate such as ethylene carbonate; a dialkyl carbonate such as diethyl carbonate, dimethyl carbonate or methylethyl carbonate, various alkyl ethers; various cyclic esters; various mononitriles; dinitriles such as glutanitrile; symmetric or asymmetric sulfones, as well as their derivatives; various sulfolanes, various organic esters and ether esters having up to 12 carbon atoms and the like.

Examples

In the following Examples, cathodes and cells were manufactured and subjected to thermal tests to evaluate the thermal stability of the cathode composition of the invention and the cells obtained therefrom.

The materials used in the cells are identified below. All percentages are percentages by weight unless otherwise indicated. All physical properties and composition values are approximate unless otherwise indicated.

"LMO-1": lithium metal oxide available from Daejeon Energy Materials Co., and having the chemical formula LiNi0.5Mn0.3Co0.2O2y with a D50 particle distribution of 10.41 pm.

"LMO-2": lithium metal oxide available from Xiamen Wuye Co., and having the chemical formula LiNi1 / 3Mn1 / 3Co1 / 3O2.

"LMFP-1": lithium metal phosphate available from Dow Chemical and having the formula LiMnFePO4 and with a D10, D50 and D90 of 0.984 pm, 3.056 pm and 7.074 pm, respectively. The volume fraction of secondary particles having a size of 0.1 to 3 microns is 49.8%.

"LMFP-2": lithium metal phosphate available from Dow Chemical and having the formula LiMnFePO4y having a D10, D50 and D90 of 5.536 pm, 9.9947 pm and 17.28 pm, respectively. The volume fraction of secondary particles having a size less than 3 microns is 0%.

"CA": conductive carbon additive commercially available under the trade name SUPER P ™ Li from TIMCAL.

"PVDF": polyvinylidene fluoride as a binder and available from Solvay Specialty Polymers under the trade name SOLEF® 5130 PVDF.

"NMP": N-methylpyrrolidone (98.5% anhydrous) available from J&K Chemical.

"Electrolyte-1": electrolyte solution of a 1 molar LiPF6 solution in a 1: 3 by weight mixture of ethylene carbonate and dimethyl carbonate, available from China Energy Lithium Co., Ltd.

"Electrolyte-2": electrolyte solution commercially available under the product name TK032, and available from BASF.

In all of the following examples, particle sizes were measured using a Beckman Coulter LS 13 laser diffraction particle size analyzer.

Inventive example 1:

LMO-1 was mixed with LMFP-1 as follows to prepare the active cathode material. LMO-1 and LMFP-1 were mixed manually in a cup in a ratio of 80:20 to make the active cathode material. The resulting active cathode material was mixed with binder (PVDF), conductive carbon (CA) and solvent (NMP) to prepare a suspension of the active cathode material.

The suspension was coated using a doctor blade on aluminum foil (20 gm thick) available from Shezhen Fulaishun Electronic Material Co. After coating, the NMP was removed by drying at 80 ° C for 30 minutes and then further vacuum dried at 130 ° C for 10 hours. Cathode wafers were prepared by cutting 12 mm diameter samples from the dry cathode. The cathode wafers were built into CR2016 button cell batteries. The anode in each case is lithium (in the case of a half cell) and a commercially available graphite, (FT-1 powder obtained from Jiangi Zicheng, Co.), (in the case of a full cell). A commercially available separator is used with an electrolyte (Electrolyte-1) of a solution of molar LiPF61 in a 1: 3 by weight mixture of ethylene carbonate and dimethyl carbonate.

Half of the coin cell was charged using a constant current (1/10 C rate) at 4.3 V, and then held at a constant 4.3 V voltage at C / 100 current. The cell was then discharged at 0.1 C to 2.8 V. The charge / discharge cycle was repeated twice and finally the cell was charged at a constant current of 0.1 C to 4.3 V and it was maintained at a constant voltage of 4.3 V at a current of C / 100.

The thermal behavior (DSC) of the charged cathodes (4.3 V) was evaluated. The fully loaded cell was disassembled in a glove box. The cathode wafer was removed and washed three times with di-methyl carbonate (DMC) and dried in the glove box for 24 hours. 1.5 mg of cathode powder was removed from the dry wafer and placed in a stainless steel high pressure DSC cell and loaded with 1.5 mg of Electrolyte-1. The cell was then hermetically sealed for DSC testing.

DSC was performed from room temperature to 350 ° C at a ramp rate of 5 ° C / min. The maximum heat release temperature and total heat release are summarized in Table 1 below.

Bag cells were prepared comprising the active cathode material of Example 1 of the invention.

Cathode material comprising 93% by weight of active materials, 4% by weight of binder (PVDF) and 3% by weight of CA as conductive additives was prepared by coating a suspension of the cathode material in NMP on Al foil (20 gm of thickness). The solvent was removed by drying successively at 80 ° C for 2.5 minutes, 95 ° C for 2.5 minutes and 90 ° C for 2.5 minutes. The dried cathode was then vacuum dried further at 120 ° C for 12 hours. The cathode was then pressed with a roller press at an applied pressure of between 125 and 130 tons to a density of approximately 3 g / cm3. The pressed cathode was vacuum dried again at 120 ° C for 12 hours. The cathode was then cut and mounted in 10Ahr, 20Ahr, 30Ahr, and 40Ahr bag cells. The anode was a commercially available graphite (FT-1 powder obtained from Jiangi Zicheng, Co.). A commercially available separator with an electrolyte (Electrolyte-2), TK032 available from BASF, is used.

The electrochemical properties of the manufactured bag cell were carried out in the Arbin test station, with the procedure set out below. The specific discharge capacity at 0.3 C is summarized in Table 2 below.

1) Rest 24 hours at 38 ° C

2) 1st load: 0.02 C 8 h, 0.1 C 1 h, 0.5 C at 4.2 V, cutoff C / 20.

3) 1st discharge: 0.5 C to 3.0 V

4) 2nd charge: 0.5 C to 4.2 V, cutoff C / 20, aging at 80 ° C for 6 h.

5) 2nd discharge: 0.5 C to 3.0 V

6) 3rd charge: 0.3 C to 4.2 V, cutoff C / 20

7) 3rd discharge: 0.3 C to 3.0 V

8) 4th load: 0.3 C to 4.2V, cutoff C / 20

9) 4th discharge: 0.3 C to 3.0V

10) 5th charge: 0.5 C 1 hour, end.

The bag cell after the EC test was discharged at 1 C at 3.0 V, followed by a charge at a constant current of 1 C at a voltage of 4.2 V and a constant voltage at a current of C / twenty. The loaded bags were then subjected to a nail test to evaluate the thermal stability of the cathode material of the invention.

Nail penetration was performed at room temperature, with a 3 mm diameter nail and a penetration rate of 80 mm / s. The results are summarized in Table 3 below.

All tested 20Ahr and 30Ahr bag cells passed without smoke or fire. The existence of small-sized LMFP particles surprisingly increased the thermal stability and safety of a lithium-ion battery. Inventive example 2

In this Example, half cells were prepared as in Example 1, except that the lithium metal phosphate comprised a mixture of LMFP-1 and LMFP-2 in a ratio of 1: 1. The resulting cathode material had a total weight ratio for LMO: LMFP-1: LMFP-2 of 80:10:10. The mixture of LMFP-1 and LMFP-2 had a particle distribution of D10, D50, and D90 of 1.658 gm, 5.882 gm, and 14.13 gm, respectively. The volume fraction of secondary particles having a particle size of less than 3 gm was 24.9%.

The thermal properties of the cathode were evaluated using the same procedures as set forth in Example 1.

Inventive example 3

In this Example, a cathode was prepared as in Example 1 with the exception that LMO-2 was used instead of LMO-1. The particle size distribution of LMO-2 was measured as described above. LMO-2 had a D50 of 10.14um. The active material was prepared by mixing LMO-2 with LMFP-1 by hand in a cup with a weight ratio of 80:20.

Bag cells comprising the cathode of Example 3 were prepared with the same experimental procedures described above for Inventive Example 1. 10Ahr, 20Ahr, 30Ahr and 40Ahr bag cells were made. The evaluation of the electrochemical properties and the nail penetration tests were accordingly carried out following the same procedure and condition as in inventive example 1. The results are summarized in Table 3 below.

All tested 20Ahr and 30Ahr bag cells passed without smoke or fire. Two 40 Ahr cells were prepared in which one passed the test and the other generated smoke. Although one of the 40 Ahr cells generated smoke, overall tests show that lithium metal phosphate with particle sizes of less than 3 gm can surprisingly increase the thermal stability and safety of the lithium ion battery. The test results are summarized in Table 4.

Comparative Example 1

In this example, a cathode was prepared using LMO-2 and LMFP-2. As in inventive example 1, the materials were mixed in a ratio of 80:20. The blending was done manually in a cup.

The particle size distribution of LMFP-2 was measured as in Inventive Example 1. LMFP-2 had a D10, D50 and D90 particle size distribution of 5.536 gm, 9.947 gm and 17.28 gm, respectively. The volume fraction of particles below 3 gm in LMFP-2 is 0%.

Thermal properties were evaluated with the same experimental procedure described in Example 1 of the invention and are summarized in Table 1 below.

Bag cells comprising the cathode of Comparative Example 1 were prepared with the same experimental procedures described above for Inventive Example 1. 10Ahr, 20Ahr and 30Ahr bag cells were made. The evaluation of the electrochemical properties and the nail penetration tests were consequently carried out following the same procedure and condition as in the inventive example 1. The results are summarized in Tables 2 and 3 below.

As can be seen in Table 3, for the two 20 Ahr bag cells prepared, one generated smoke and the other generated fire. A 30Ahr bag cell was tested, which generated fire. From these results, compared to the results of Inventive Example 1, it can be seen that cathode materials having a distribution of Smaller particles for the lithium metal phosphate component (eg, a 5-100% volume fraction with a particle size of less than 3 pm) can provide improvements in thermal stability and safety in a LIB.

Comparative Example 2

In this example, an active electrode material was made by mixing LMO-2 and LMFP-2 by hand in a cup in an 80:20 weight ratio. All other components, percentages and procedures remain the same as in Inventive Example 1.

Bag cells comprising the cathode of Comparative Example 2 were prepared with the same experimental procedures described above for Inventive Example 1. 10Ahr, 20Ahr and 30Ahr bag cells were made. The evaluation of the electrochemical properties and the nail penetration tests were consequently carried out following the same procedure and condition as in the inventive example 1. The results are summarized in Tables 2 and 3 below.

For two 20Ahr bag cells prepared, one generated smoke and the other generated fire. A 30Ahr bag cell was tested, which generated fire. As discussed above, the lack of particles having a size below 3 pm resulted in a LIB that had poor thermal stability and safety.

Table 1: Particle size distribution and thermal data (DSC)

Table 2: Discharge capacity and press density of the cathode material

Table 3: Nail penetration performance

Claims (11)

1. A method of forming a cathode comprising: (a) mixing a lithium metal oxide and a lithium metal phosphate in a solvent, wherein the lithium metal phosphate has a volume fraction of secondary particles having a size of 0.1 to 3 microns that it is 5 to 100%, based on the total content of the lithium metal phosphate; and where lithium metal phosphate has the formula: Li1 + aMnbFecM1-b-cPO4, Formula (I) where: a is a number from 0.0 to 0.2, and preferably from 0.0 to 0.15, and more preferably from 0 to 0.12; b is a number from 0.05 to 0.95 and preferably from 0.1 to 0.9 and more preferably from 0.2 to 0.8; c is a number from 0.05 to 0.95 and preferably from 0.1 to 0.9 and more preferably from 0.2 to 0.8; and (1-b-c) is 0.0 to 0.2, and preferably 0.0 to 0.15, and more preferably 0.0 to 0.12, where M is a metal ion selected from one or more of magnesium, calcium, strontium, cobalt, titanium, zirconium, molybdenum, vanadium, niobium, nickel, scandium, chromium, copper, zinc, beryllium, lanthanum and aluminum, and the oxide of lithium metal has the following formula: LiXNiyMnzCo ( ² -xyz) DwO ² , Formula (III), or LiXNiyMnzCo ( ² -xyz) O ² where: x is a number from 0.9 to 1.15, and preferably from 0.95 to 0.110, and more preferably from 0.98 to 1.08; y is a number from 0.05 to 0.95, and preferably from 0.2 to 0.95, and more preferably from 0.3 to 0.95; z is a number from 0.05 to 0.95, and preferably from 0.05 to 0.8, and more preferably from 0.05 to 0.7; (2-x-y-z) is 0.05 to 0.95, and preferably 0.05 to 0.8, and more preferably 0.5 to 0.7, and w is 0 to 0.4, and preferably 0 to 0.3, and where D, when present, is selected from the group consisting of B, Al, Ti, Mg, Nb, Si, Fe, V, Cr Cu, Zn, Ga and W, and is preferably selected from the group consisting of Al, Ti, Mg and Nb (b) coating the mixture of step (a) on a metal foil; and (c) remove the solvent to form the cathode wherein a D50 of the lithium metal phosphate is equal to or less than 3.5 microns. The method of claim 1, wherein the volume fraction of secondary particles having a size of 0.1 to 3 microns is at least 50%, based on the total content of lithium metal phosphate. The method of claim 1, wherein a D50 of the lithium metal phosphate is equal to or less than 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3 , 1.3.2, 3.3 or 3.4 microns. The method of claim 1, wherein the lithium metal phosphate comprises a mixture of two different lithium metal phosphates with a first of said lithium metal phosphates having a volume fraction of secondary particles having a size of 0.1 to 3 microns that is at least 20%, and the second of said lithium metal phosphates has a volume fraction of particles having a size of 0.1 to 3 microns that is 0%, and wherein the lithium metal phosphate mixture has a collective volume fraction of secondary particles having a size of 0.1 to 3 microns that is at least 20%, based on the total lithium metal phosphate content . 5. A cathode material comprising a lithium metal oxide and lithium metal phosphate in a solvent, wherein the lithium metal phosphate has a volume fraction of secondary particles having a size of 0.1 to 3 microns which is 5 to 100%, based on the total content of lithium metal phosphate, in which a D50 of the lithium metal phosphate is equal to or less than 3.5 microns and in which the lithium metal phosphate has the formula: Li1 + aMnbFecM1-b-cPO4, Formula (I) where: a is a number from 0.0 to 0.2, and preferably from 0.0 to 0.15, and more preferably from 0 to 0.12; b is a number from 0.05 to 0.95 and preferably from 0.1 to 0.9 and more preferably from 0.2 to 0.8; c is a number from 0.05 to 0.95 and preferably from 0.1 to 0.9 and more preferably from 0.2 to 0.8; and (1-b-c) is 0.0 to 0.2, and preferably 0.0 to 0.15, and more preferably 0.0 to 0.12, where M is a metal ion selected from one or more of magnesium, calcium, strontium, cobalt, titanium, zirconium, molybdenum, vanadium, niobium, nickel, scandium, chromium, copper, zinc, beryllium, lanthanum and aluminum, and the oxide of lithium metal has the following formula: LiXNiyMnzCo ( ² -xyz) DwO ² , Formula (III), or LiXNiyMnzCo (2-x-y-z) O2 where: x is a number from 0.9 to 1.15, and preferably from 0.95 to 0.110, and more preferably from 0.98 to 1.08; y is a number from 0.05 to 0.95, and preferably from 0.2 to 0.95, and more preferably from 0.3 to 0.95; z is a number from 0.05 to 0.95, and preferably from 0.05 to 0.8, and more preferably from 0.05 to 0.7; (2-x-y-z) is 0.05 to 0.95, and preferably 0.05 to 0.8, and more preferably 0.5 to 0.7, and w is 0 to 0.4, and preferably 0 to 0.3, and where D, when present, is selected from the group consisting of B, Al, Ti, Mg, Nb, Si, Fe, V, Cr Cu, Zn, Ga, and W, and is preferably selected from the group consisting of Al, Ti, Mg, and Nb 6. The cathode material of claim 5, wherein the lithium metal phosphate comprises a volume fraction of secondary particles having a size of 0.1 to 3 microns that is at least 20%, based on the content total lithium metal phosphate. The cathode material of claim 5, wherein the lithium metal phosphate comprises a volume fraction of secondary particles having a size of 0.1 to 3 microns that is at least 50%, based on the content total lithium metal phosphate. 8. The cathode material of claim 5, wherein a D50 of the lithium metal phosphate is equal to or less than 2.5, 2.6, 2.7, 2.8, 2.9, 3.0 , 3.1, 3.2, 3.3, or 3.4 microns. 9. The cathode material of claim 5, wherein a D50 of the lithium metal phosphate is equal to or less than 3.1 microns. The cathode material of claim 5, wherein the lithium metal phosphate comprises a mixture of two different lithium metal phosphates, wherein a first lithium metal phosphate comprises a 20% volume fraction of secondary particles having a size of 0.1 to 3 microns, and A second lithium metal phosphate comprises a 0% volume fraction of secondary particles having a size of 0.1 to 3 microns, and wherein said lithium metal phosphate mixture has at least a volume fraction of the 20% secondary particles having a size of 0.1 to 3 microns. 11. A lithium ion battery comprising the cathode of any one of claims 5 to 10.